A full RDS (Removable Deployment System) involves removing your slider, d-bag and pilot chute after opening. You can read about how the RDS works here.
A removable slider means you take off ONLY the slider after opening, and it isn't connected to your d-bag and pilot chute, which remain attached to the tail of your canopy as normal. A removable slider is the simpler of the two options, allowing you to quickly free up some drag and spread the risers. It's a lot quicker to pack and causes less problems for malfunctions.
The full RDS is only for highly experienced pilots on high performance wings - probably best only used for competitions and XRW, where reduction of drag is most critical.